1. Field of the Invention
The present invention relates to a media feeding apparatus which feeds a stacked sheet-like medium to a processing apparatus. Especially, the present invention relates to a media feeding apparatus for image forming apparatuses such as copiers, printers, fax machines, etc and an image forming apparatus including the media feeding apparatus.
2. Description of the Background Art
Conventionally, a media feeding apparatus which separates and feeds stacked sheet-like media one by one has been known. This media feeding apparatus has been used for image forming apparatuses such as copiers, printers, etc.
These image forming apparatuses have a sheet feed cassette or a sheet feed tray which stacks sheet-like media for forming an image on the media (such as papers and sheets for overhead projectors) and feeds them into the image forming apparatus.
Recently, media for the image forming apparatuses have diversified due to the spread of color copiers, color printers and such. Non-plain paper, such as a coated paper, art paper, film lined paper, thick paper, and extra-thick paper (Kent paper, etc.) have been used in image forming apparatuses. These types of paper have features such a high smoothness of the surface and high hygroscopic nature. When these types of paper are in a stack, the negative pressure between the papers causes a strong adherence force between the papers. As a result, the separability of the papers is poor and causing problems such as multi-feeding and miss-feeding, instead of the papers being separated one by one and fed into the image forming apparatus. This problem occurs not only with paper but also with other materials which have a high adherence force such as sheets for overhead projectors.
Moreover, a similar problem may occur as a result of the condition of the stack which causes the adherence force to be high. As described above, in the stack of media which has a high adherence force such as more than about 100 gf the media is not able to be separated one by one by typical rollers of a media feeding apparatus because the media sticks together.
Japanese Patent Application Laid-Open No 1999-5643 (referred to as related application 1) describes a technique of feeding media one by one correctly from such a media stack.
In this application, air flow is controlled such that the upper side of uppermost sheet has negative pressure. Thus, the sheets are separated one by one by this lift force toward the upper side of the sheets as a result of the negative pressure.
In addition, in a technique for a media feeding mechanism which improves separation performance by air flow, Japanese Patent Application Laid-Open No 2003-63675 (referred to as related application 2) discloses that a floatation suppression member is arranged between air outlets and a sheet feeding roller to suppress a degree of sheet lift.
In this application, the sheet feeding apparatus is arranged so that sheets are steadily separated and stably fed one by one regardless the sheet size in the sheet feeding apparatus described in the related application 1. In this invention, the upper few sheets of the stack are floated with gap between the sheets and separated one by one even though the sheets have high adherence force due to the floatation suppression member arranged between the air outlets and the sheet feeding roller.
However, related application 2 is not able to obtain enough floatation suppression with respect to the air flow because the floatation suppression members are mounted on lateral adjusting members (i.e., side fences). That is to say, as shown in FIG. 1, the air blown by fan 501a via an outlet disposed in side fence 502 directly contacts the air blown by fan 501b via an outlet disposed in the other side fence 502 forcing the air to blow towards near the center of the sheet P held by the side fences 502 and an end fence 503. The air is then changes flowing direction and flows forward with respect to the sheet feeding direction. The air flowing forward with respect to the sheet feeding direction then contacts a feeding roller 505 pressing sheets via narrow space A between floatation suppression members 504 mounted on the side fences 502. The air then flows around the feeding roller 505 and out to in front of the sheet from the side of the feeding roller 505 (the direction is shown by the arrow B in FIG. 1). Because of this air flow, the sheet P is made to float at the side portion of the feeding roller 505 arranged at forward portion of the sheet with respect to the sheet feeding direction. Thus, the feeding resistance of the sheet P is increased due to the floatation and there is caused a conveying malfunction in that the feeding roller 505 is unable to feed the sheet correctly (i.e., paper jam).
As described above, the techniques disclosed in the related applications does not consider the influence of air flow. As a result of this oversight, subsequent feeding of sheet is negatively influenced so that sheet separation by air flow is reduced.